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Date: Sat, 5 Jan 2013 16:37:34 +0800 From: Alex Shi <alex.shi@...el.com> To: mingo@...hat.com, peterz@...radead.org, tglx@...utronix.de, akpm@...ux-foundation.org, arjan@...ux.intel.com, bp@...en8.de, pjt@...gle.com, namhyung@...nel.org, efault@....de Cc: vincent.guittot@...aro.org, gregkh@...uxfoundation.org, preeti@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org, alex.shi@...el.com Subject: [PATCH v3 05/22] sched: remove domain iterations in fork/exec/wake Guess the search cpu from bottom to up in domain tree come from commit 3dbd5342074a1e sched: multilevel sbe sbf, the purpose is balancing over tasks on all level domains. This balancing cost much if there has many domain/groups in a large system. And force spreading task among different domains may cause performance issue due to bad locality. If we remove this code, we will get quick fork/exec/wake, plus better balancing among whole system, that also reduce migrations in future load balancing. This patch increases 10+% performance of hackbench on my 4 sockets NHM and SNB machines. Signed-off-by: Alex Shi <alex.shi@...el.com> --- kernel/sched/fair.c | 20 +------------------- 1 file changed, 1 insertion(+), 19 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index ecfbf8e..895a3f4 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3364,15 +3364,9 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags) goto unlock; } - while (sd) { + if (sd) { int load_idx = sd->forkexec_idx; struct sched_group *group; - int weight; - - if (!(sd->flags & sd_flag)) { - sd = sd->child; - continue; - } if (sd_flag & SD_BALANCE_WAKE) load_idx = sd->wake_idx; @@ -3382,18 +3376,6 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags) goto unlock; new_cpu = find_idlest_cpu(group, p, cpu); - - /* Now try balancing at a lower domain level of new_cpu */ - cpu = new_cpu; - weight = sd->span_weight; - sd = NULL; - for_each_domain(cpu, tmp) { - if (weight <= tmp->span_weight) - break; - if (tmp->flags & sd_flag) - sd = tmp; - } - /* while loop will break here if sd == NULL */ } unlock: rcu_read_unlock(); -- 1.7.12 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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